Cavity resonator



July 26, 1949. D. E. BRANsoNL CAVITY RESONATOR Filed March 28,y 1945 R N50/v ATTORNEY @QSL DEB

Patented July 26, 1949 CAVITY RESONATOR David E. Branson, River Edge, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application March 28, 1945, Serial No. 585,286

3 Claims.

This invention relates to an organization comprising tunable, magnetically coupled, cavity resonators and also to collateral elements contained therein affecting the tuning and coupling charl acteristics;

A comprehensive object of the invention is to achieve an organization as above which has the maximum flexibility `and versatility and therefore is most adaptablefor use in a variety of electrical environments such as oscillators, amplifiers, Wave meters and the like, all requiring two or more tunable cavity resonators. The object may be realized, as herein, in an organization in which there may be either Van individual or a simultaneous tuning of said resonators while preserving initial desirable characteristics of said resonators as to impedance and radiation characteristics and the like, and with a desired predetermined quantity and kind of coupling therebetween. These results are largely achieved by the plunger and dirigible coupling loop to be referred to below which also, however, have capabilities of use independently of the general organization.

A subsidiary object of the invention is, in a tunable cavity resonator where tuning is a function of the movement of a plunger to'correspondingly vary the axial dimension of the resonator,

'to provide an electromagnetic seal between the plunger and contiguous resonator wall having optimum electrical contact resistance character-- istics at the same time as insuring a minimum of electromagnetic radiation leakage between said plunger and walll Another subsidiary object is to provide a simple, variable, energy coupling means between a pair of said Vresonators which, consistently with extreme simplicity, is capable of continuous variation in degree of coupling and of choice of coupling as between positive or negative. These yterms positive. and negative achieve theirspecial meanings only in connection with the or- 'ganization as a Whole in which said pair of res- 'tion in which the coupled resonators are constituted by the interspaces in a triple-conductor Ieoaxial system. In practice the inner middle and tors are connected respectively to the anode, control electrode, and cathode, respectively of an electron tube which cooperates with the coaxial to constitute the whole, an oscillator. The two resultant concentric annular-shaped, cavity resonators are made completely closed, as is necessary in practice, by a common, xed end closure member at one, common, end and at the oppo- .site ends by movable piston-like plungers Whose axial positionsv determine the eiiective lengths of the respective resonators and hen-ce their frequencies. These two plungers, which of course Y are annular like the cross-sections of the related resonatorsand are concentric with each other, are coupled together and to a common operating mea-ns. This operating means is in the form of a plurality of rods which are constrained to move axially of the resonator and are screw actuated to adjust the two plungers as a unit. The system of actuating rods is divisible into rods speciiic to each said plunger and screw means are outer concentric cylinders bounding the resona- 55 within the inside walls of the resonators.

adapted to operate one component set with relation to the other so as to achieve a relative adjustment of the two plungers. The organization as a Whole therefore is adapted to achieve any desired adjustment of the plungers. 'Ihe principle, of course, may be readily adapted to a greater number of resonators and plungers, which themselves may be adapted to a` versatility of shapes and cross-sections.

One of the two specific features' which round out and make the organization as a, whole effective under the adverse conditions imposed is a means for sealing the peripheries of the plungers This comprises avspecial element interposed between each tuning plunger andits cooperating wall to insure not only a low resistanceelectrical connection therebetween during movement of the plunger but a complete closure so as to minimize loss by electromagnetic leakage radiation. The relation between plunger, and resonator wall par.. takes of the obviously quite non-analogous function and structure of a piston ring and cylinder of an internal combustionfengine and the special element therefore resembles a piston ring. It differs radically from it in texture (as of course it does for other reasons in its over-all purpose) because of being non-rigid. It is made of fabriclike material with elastic backing that might be provided by rubber, vegetable fiber or the like. The fabric-like material, of course, must be conducting so that it partakes of the character of a braided shieldof a shielded conductor or cable. This means will be described in the detailed de- 3 scription to follow and in the claims by use of Such terms as plunger packing and packing ring.

The prior art is replete with would-be alternatives which have not been entirely satisfactory in practice. These have most -commonly taken the form of spring iingers attached to the plunger .and extending from them in an axial direction, their outer extremities, Vof course, bearing on the inside walls of the cooperating resonator. Sometimes a Wire helix is used in a peripheral groove, which helix may even, as in the presenti-invention, be compressed to squeeze it tightly against the resonator wall. Even'metalbal-ls conned in a race, as for ball bearings, have been used. These expedients all involve comparatively rigid movable contacts or bearing elements; Thepacking of the invention has certain specific advantages over these alternatives, especially the spring lingers which perhaps come closest in their desii-'able attributes, which can perhaps be better mentioned here than in the detailed' description, these advantagesbeing of extremely great significance as trequentty making a particular installatior-i practicable whenit would otherwise. be

impracticable.

Ew). The wear afterlong continued use is very much less` and even. ati the extrem-e tends to be .proportional rather than ito be Ysubject to the hazardof an unexpected complete breakdown.

(mi Since the fabric-like plunger packing of the invention so easily accommodates itself to imposed conditions as compared withzitsi alterna- Y tives, its; use obviateszthe. holding of the. resonator tubes; toy asf exact dimensions as.; would otherwise be required.V

. (Ic). ''llhefqualitiesY of good electric conduction and' high elasticity inv spring lingers or the: like are antitheticalf so. that the ingers,` ata resultant increased' expense, must be plated with conducting' material that will be. retained, a diftls-zult@ combination of requirements. Also the spring.' -ngersmust be. long enough to properly vguilde they springs without binding or injuryy and 'this-tends to increase the .over-all length of the resonator. Since spring fingers. themselves. partake of the characteristics of a transmission line otherwisebe required and which at the best would tend tol introduce or increase the'- seriousv disadvantages that have been mentioned.

(d) Besides the fact that the` packing of the invention results in a smaller contact resistance than in its alternatives including the spring fingers, the use of the spring fingers tends to. result in capricious changes in its contact resistance to obviatewhich requires a certain inconvenient and tedious discipline in the adjustment of the plnngers during. reversal of direction of adjustment. For instance it. was. found to. be. always necessary to approach the desired plunger setting 'from the same direction since anovershoot could.,

not be corrected merely by reversingl the direction of, the control.V With thepresent considered packing, there is no comparable eiect.

(e) The above-v advantages and' the other' ad- Axraizitages tof be cited are not only not attended by 4 compensatory increased cost but the use of the packing causes the organization as a whole to distinctly cost less than when any of its alternatives are used.

(f) The packing results in a more complete closure so that the magnetic leakage is definitely less than in the alternatives. The leakage has two walls to go through inthepacking hence the 'shielding effect is double that of 'spring fingers and there are no spaces, corresponding to the spaces between the spring fingers, yfor leakage.

The4 organization as a whole is perfected in its iexibility and versatility of use by the variable coupling' feature-whereby the resonators are adequateliyi-ntercoupled. In any one adjustable position of this coupling, the effect may not be much dierent from that achieved by the prior art means, usually comprising a simple loop in one resonator connected to a like loop in the other. However, in this instance the two loops are rigidly interconnectedsto form Aa; ngi-.1re roughly the equivalentwofr a conventionali'zed gure: 8 .or letter S (thought of `resting oir their sides instead of beingzupriglmtz.) means ifor rotating the combination about a line corresponding to: the verticali aixiszoi' thise'nigureor letter;l lu'rtherxrrore;l the two loops constituting the: gureorletter are not in a common plane: but one-.is twisted'oir skewe relatively to. the. other 'about tlzsaxis'which will Ice-denominated the skew axis by about 120" degrecs; 'IrhisL-meansithat. depending onthe particularirotational adjustment/of, theloopas; a whole allientl thissame axis, the coupling maybe made tof partake ot the .characteristics lof ya positive'or a negati-ve couplingy at will, with a range of variationfoiieach. As aiectingrtheoperationfofam osciililatory of the resonators are; a. part, the

i or feedback.k A flat-loop` ('botlcomponient loops in same planer): wowl'ii give,t either positivetor. negative ieedbaokin :adjustable-amount but; not yadjustable from-positive to@ negatives. If. the cornponent loopsirare warped.' outfof the'samelplane, as the invention,` they mayv be adjusted: from a maximum negative to `a maximum `positive feedbackV sinootl'ily.

The currentsl on thevopposite walls of the. grid tubecausev the respectivemagnetic eld in. the two cavities tobe directions.` reversed; to.- each other, The projected. cross-section of the.= loop, when. said loopi is positioned :so-'that' the: crosssection is S shaped indicates a coupling to: aidi'or strengthen the normal 'rela-tions; 'or the magnetic 55, fields. to be known as; positives feedback, and when the projectedcross-section of. thel loop is 0' or'D shaped indicates a couplingv tooppose or weaken the noi-'mai relation. or the magnetic: 'ilelrls` to be known as negative feedback. The above indications assume that-the coupling loop'y has therphysical appearance of a. conventionalized letterv S al- Y though am analogous condition. would applly if itA more nearly vresezinbled'a: conventionalized gure-8. Y

Animportant. incidentalf effect of .this coupling is that at the proper location (see. detailed description) lthe double; resonator organization as used". an oscillator yor Aamplier may be made tof function smoothly over 'a greater practicable range of frequencies than with prior alternativesit the: feedback may be adjusted' to suit4 the extreme; ends or `the range, this for an ampliiler possiblyI sometimes reduiringa change from positive-to negative. feedback-or viceversa.. lnzapra'ctical .case it, is. .posoiblatoigetlonly asl much-as a 2 to 1 range with it in a fixed position whereas if adjusted the range might well be increased to -a coaxial resonator system embodying the features of the invention;

Figs. 2 and 3 are cross-sectional views at lines 2--2 and 3 3, respectively;

Fig. 4 illustrates in cross-section a fragmentar7 part of the Figs. 1 to 3 organization, specically of the inner tube and plunger in order to disclose in greater detail the packing of the invention and its compressing means;

Figs. 5 and 6 comprise graphic devices, although in the nature of a transverse elevation View of the coupling loop, to illustrate the operation of the loop and its eiect in different adjusted positions; and

Fig. 7 illustrates said coupling loop and its immediate structural environment in perspective.

'Referring now to the drawings, and especially to Figs. 1, 2 and 3 which show the organization as a whole, the three metallic tubes (the material might well be brass, although there is a considerable choice), I, 2 and 3 constitute a coaxial conductor system and by their interspaces determine the two cavity resonators here concerned,

these resonators being completed by rigid heading, or main assembly plug, 4 and axially adjustable annular disc-like plunger elements 5 and 6. In a particular over-all organization in which these resonators have been successfully used in practice and as is suggested by the fragmentary showing of the associated electron tube at the right in Fig. 1, these tubes I, 2 and 3 are attached respectively to the anode, grid, and cathode of an electron tube, the whole organization, with the help of the magnetic coupling between the resonators which will be commented on presently, constituting an ultra-high frequency feedback oscillator of a quite common generic type.

The main assembly plug 4 is integrally attached, as by soldering, to the central tube I and tubes 2 and 3 may most appropriately be connected to said plug by separable connections as by the screw threaded means shown. Figs. 1, 2 and 3, which are at present under consideration, show, although the details will be discussed in connection with other figures, two important subsidiary features of the organization and which enable the two or more resonators to be most effective in the over-all organization in which said resonators are used. These are the plunger packing means 1, an instance of which occurs at each of the four places of contact between the plungers and adjacent resonator walls, and the dirigible feedback coupling or loop 8.

` stitute a part of the invention. As here shown it should preferably be close to the xed closure end of the resonator and, best of all, in the plane of 6. the connecting bars of the component loops of the coupling means.

Considering-now the actuating means for the plungers, and therefore the means for tuning the corresponding resonators, the inner plunger 5 is made with a loose fit over inside tube I and is pushed by three rods such as rods I0 of Fig. l, the others being uniformly with it distributed about the common axis and as shown in section in Fig. 2. These rods are attached remotely from the plunger to guide, or push, plate II. They are attached to the plunger by plate I2 thereof, constituting the major part of the disc-like plunger. rlhe plunger packings I are squeezed against the adjacent tube (resonator) lwall within the triangular spaces bounded by the bevel edges of said plate I2 and cooperating plate I3. Of course the conformity of the wall bounding this space is not critical and could differ widely from the triangular conformity shown. The desired force is obtained by adjusting screws I4 threaded through plates I2 and I3. The screws are reached through holes I5 in the plug 4. The screw heads are shown in sectional view Fig. 2 which indicates that, in the particular arrangement here disclosed, three such adjusting screws are used (nine similar screws being shown for the outer plunger). These adjustments are made when the plungers are all the way to the left. The plunger disc is maintained radial since it slides on tube I and the relationship of the rods I0 to said tube I is made constant by the con straint of their movement through iixed holes in said plug 4. I'he rods would determine the effective length of the plunger as a unit. The fact that the guide plate II must be outside o-f the support for the tubes, that is, outside of the resonators, need not aplpreciably change the overall length of the resonator assembly or oscillator.

`As has been pointed out in the statement of invention, said over-al1 length is considerably less than if spring fingers were used instead of the packing of the invention.

The outer resonator has a similar plunger operating means, comprising rods IE and guide plate I'I. These elements are related to said cooperating elements precisely as in the instance of the innermost resonator and like structural elements have like labels.

The operating means for the two plungers are linked together by differential screw means I8 to make possible any specific adjustment of either plunger without necessary affect on the other plunger. The main drive, which is common to both plungers and sets of driving rods, is from stationary block I9 which is fixed to the inner- Vmost tube I, by screw 20 through guide plate II.

various applications of this double resonator system and particularly in its application to the oscillator here in mind.

Although the attachment of the grid and anode tubes to the electron tube is shown as by means of spring lingers or the like, the attachment of the cathode tube must be more positive because this is the principal reliance for the attachment of the electron tube and resonator assembly as a whole and accordingly a packing similar to that used for the plungers may be used and ishere illustrated.V The packing is similari-,o the extent that it also requires the braided copper or the like outer element to provide a good conductive since been found not to be essential.

connection but the resilent core may be made harder so that a more rigid grip Vvmay be obtained to more denitely hold the tube in place. The element corresponding to plate i 3 of the plunger assembly is integral with the electron tube assembly so that the clamping of the cathode tube against it through the intermediation of the packing satisfies the requisite condition of rigidity. :Since the junction of the vcathode tube, through the packing, to the electron tube is the important consideration the plate corresponding to element 'i3 of the plungers need not be conductive at this particular junction.

The packing element itself is best shown in Fig. 4 which shows in section a portion of the inner resonator adjacent the plunger. f The packing 'has the physical appearance of va section of `cable of a particular kind, namely, with a single center conductor covered by a small amount of rubber insulation, in turn covered by a double cotton braid and finally by a tinned-copper braided shield. In an actual installation which proved to be effective in practice the packing was made up in this way, the lbraided shield being taken from a shielded conductor and having inserted in it a portion of a cable comprising the other elements including a 19-gauge conductor,

-the outer diameter being about 1A; inch. Of

course the outer braid serves Vas the conductive connection and if the copper is hard, it contributes a considerable spring action by itself, although laterexperience has shown that soft copper is nearly as good and that its tinning is not essential. Th'e only utility -of the inner conductor and insulation is to satisfy a presumed requirement strength since the packing is quite tightly Wrapped around the plunger. However, this has The cotton braid and rubber serves as a cushion for, and gives a soft support to, the copper braid. In practice the packing is wrapped` around the plunger and cut off the proper length to insure a reasonably tight butt joint, but'the ends are not Vsoldered together. The packing is lthen tightened to the desired amount With the plungers pulled all the way out so as to line up r'the packing concentrically. The packing ring is clamped quite rigidly so that the packing will be formed with the entire circumference Yof the plungers and then loosened up slightly, The

'8 :metrically positioned coupling yloops would be used and to illustrate the two extremes in their adjustment for particular purposes. In most common practice the adjustments would be ali-ke for the two loops. 1 Loop A is in regenerative adjustable position and loop B is in degenerative adjustable position. Figs. 5 and 6 are respectively related to loops A and B and show them as they would appear when looked at in the direction of the down stroke of the conventionalized S. `It is apparent that the planes of the component loops are not the same, one beingy displaced (skewed) by about 120 degrees from vthe other. This is well shown in Figs. 5 and 6 and in perspective view Fig. 7. The loop as a whole is rotatable aboutY an axis corresponding tothe direction of the down stroke lof the S that is, of the skew axis. The effect of so rotating the'loop as between regeneration and degeneration for example is determined by the relative disposition of the two component loops in the respective resonators. This relation yobviously could Anot change if the loop as a whole were in a single plane, that is, without the distortion that characterizes the loop of the invention. With the loop of the invention, it is obvious from Ythe disclosure that a radical change results from the 90 degree rotation of the loop as a whole from the position of loop A to that of loop B. For instance following the line of attack used inthe statement of invention, it is evident that in the position of loop A there is a symmetry about the down stroke element of the gure (the skew axis) whereas in the position of loop B there is a dissymmetry about the same. This is Well shown in Fig. 1. This result would come about with any deviation from a zero angle or 180 degree angle between the'planes of the component loops (the 'letter S as it appears on this sheet representing fthe 180 degree displacement). The deviation explanation of this phenomena is contained in concentricity Will then be preserved when the plungers are pushed away from the supporting l ends. Other variations than above indicated, in

the physical make-up of the packing ring, while preserving the essential characteristics of the outer non-rigid conductive element and the inner cushion, have been used. Where made up ab initio the cushion means could well have the texture of rubber and the packing material'could be constituted by only said rubber core with the braided covering. In one installation the cushion is made of varnished cambric.' In another and perhaps the one best adapted for large scale manufacturing and otherwise being at least'as eiective as the particular one here shown, a core material known/in the trade as Vinylite is used which is an extruded plastic material having the general configuration of spaghetti, in fact being the modern equivalent of spaghetti as the term is used to describe common material used in the art of electric conductors.

The coupling loops are shown in two aspects in Figs. 1 and 3 in their intended environment. Two

such loops are disclosed,V both in deference to the the statement of invention and will not be repeated at this place. The bar joining vthecom'- ponent loops would generally be coincident with the skew axis but it could, Without substantial sacrifice be at an angle with respect to the same. Also the mounting would ordinarily and preferably be such that the planes of the component loops are normal to the next adjacent walls of the tubes on Which they are mounted. Also, a1- though the simple compact structure shown commends itself to practical use the principle governing its mode of operation would be consistentwith the component loops being far separated but having the necessary integral `functional relationship by a connecting mechanical movement. f

Although specific embodiments of the invention have been shown and described, it Will be understood, of course, that they are but illustrative and that various modifications may be made therein without departing from the scope and spirit of this invention as defined in the appended claims.

What is claimed is:

1. A tunable cavity resonator. comprising a tuning plunger having its periphery conformable generally with the inner cooperatingwall of the resonator, a clamping member adjustablyrelated to said plungerand having a cut-out peripheral conformity so as to dene a space `between said plunger, clamping member and wall, and a resilient element positioned to completely electromagnetically seal the said space between said plunger, clamping member, and wall and provide a good electrical connection therebetween, said element comprising a fabric-like conductive outer member with an interior cushion of resilient material.

2. A tunable cavity resonator comprising a tubular Wall portion, a closure element at one end, and a tuning plunger comprising the remainder boundary structu-re, said plunger comprising two peripheral elements at least one of which is beveled at the corner opposite to the other, so as to define a space between the tubular wall and them-selves, means connecting said elements at a plurality of peripherally spaced points and adapted to adjust the longitudinal spacing therebetween and therefore the extent of said space, and a resilient element positioned to completely electromagnetically seal said space and to provide a good electrical connection between wall and plunger, said resilient element comprising a fabric-like conductive member with an interior cushion of resilient, non-conductive material.

3. The `structure defined in claim 2 in which said resilient element comprises a braided metal 10 sheath enclosing the cushion, the whole simulating in apearance a conductive sheathed section of insulated conductor, and adapted to .be wrapped around the plunger and compressed in the space between said relatively adjustable peripheral elements.

DAVID E. BRANSON.

REFERENCES CITED The following referenlces are of record in the le of this patent:

UNITED STATES PATENTS 

